Sheet counter head control

ABSTRACT

A counter for counting the number of sheets in a stack has a rotor (12) which engages in an edge region of the stack and transfers sheets one at a time from one side of the rotor to the other upon rotor rotation. The rotor (12) is mounted on a shaft (13) carried by a carriage (36) arranged for sliding movement on guides (41). A motor (44) drives a lead screw (43), whereby the carriage is driven along the guides. The rotor (12) may float on its shaft (13) and its position is sensed by detector (39, 40); the output of the detector is used to control motor (44) whereby the carriage is driven substantially continuously and smoothly at a rate appropriate for a counting operation being performed.

This invention concerns the counting of sheets, for example of paper,assembled into a stack. In particular, this invention relates to controlmeans for a counting head to advance the head as counting progresses.

A known form of counting apparatus employs a rotor arranged to count thenumber of sheets in a stack by engaging an edge region of the stack andthen, on rotation of the rotor, separating an edge portion of each sheetin turn from the stack and transferring the separated edge portionthrough a transfer groove to the other side of the rotor. At least onesuction port may be provided in the rotor adjacent the transfer grooveand through which port air is drawn in a timed relationship to rotorrotation, to assist the separation from the stack of the next sheet edgeportion to be counted.

The sheets to be counted are assembled into a stack which is thenlocated on a counting table, and clamped in position, ready to becounted. The edge regions--and usually a corner region--of the stackwhere counting takes place have to be able to separate to an extentsufficient to enable the rotor to be located between any two adjacentsheets in the stack. Thus, the stack must be clamped sufficiently farback from the region where counting takes place to permit this flexing.

As counting commences and sheet edge portions are transferred from oneside of the rotor to the other, the rotor has to move along the heightof the stack. In a known form of such counter, the rotor is mounted on acarriage arranged for vertical sliding movement along the height of thestack and which carriage is counter-balanced so that the rotor exerts,under gravity, a relatively small force on the stack. Then, the rotormay be allowed to move along the length of the stack merely by beingpushed by the sheets of the stack, on these sheets being transferredfrom one side of the rotor to the other.

It is also known to mount the rotor for vertical movement on a carriage,there being two limit switches at the permitted extremes of rotormovement with respect to the carriage and a motor drive arrangement tomove the carriage when the rotor triggers one limit switch, motoroperation being suspended when the rotor triggers the other limitswitch. Such motor control gives a varying engagement force between therotor and the sheets being counted, and in turn this may lead to a lackof reliability in the counting operation.

According to the present invention, there is provided control means fora linearly-movable carriage supporting a counting head arranged to counteach sheet in a stack of sheets, which counting head engages an edgeregion of the stack at one end thereof and then is advanced through thestack on transferring sheets, one at a time, to the other side of thehead and generating a count on each said transfer, the counting headbeing movable with respect to the carriage generally in the direction ofmovement of the carriage, which control means comprises a motor toeffect carriage movement, a linear sensor for the relative position ofthe counting head with respect to the carriage, and a control circuitfor the motor and arranged to cause the motor to run at an appropriatespeed having regard to the output of the sensor, whereby the carriage isadvanced substantially constantly and at substantially the same rate asthe counting head advances along the stack.

The control means of this aspect of the invention provides a linearcontrol for the carriage supporting the counting head. In this way, thecarriage may be advanced smoothly and more or less continuously as thecounting head advances along the stack and in turn this assures that theforce exerted by the counting head on each sheet of the stack, as eachsheet is picked up for transfer across the head, is substantiallyconstant.

The sensor employed in the control means of this invention may take anyone of a variety of different forms. For example, a linear potentiometermay be employed, or a LVDT. Though a digital sensor, such as an opticalencoder, could be employed, the sensor would have to have a relativelyfine resolution and be associated with a digital-to-analogue converterso as to provide a linear signal for the control circuit.

The control means may include limit switches for carriage movement, toinhibit motor operation both when the carriage has been fully liftedaway from a stack and when a counting operation has been completed. Thecontrol circuit may further include a control permitting selection of anappropriate advance rate for the counting head; this control may be usedboth to control motor speed and also to control counting head countrate.

By way of example only, one specific embodiment of counting apparatusconstructed and arranged in accordance with the present invention willnow be described in detail, reference being made to the accompanyingdrawings, in which:

FIG. 1 diagrammatically illustrates the principle of a sheet counterwith which the present invention is concerned;

FIG. 2 diagrammatically illustrates a counting rotor together with acarriage therefor, arranged for use with a control device in accordancewith the present invention;

FIG. 3 diagrammatically illustrates the control circuit for thearrangement of FIG. 2; and

FIG. 4 is a vertical part-sectional view on an alternative rotorposition detection system.

FIG. 1 illustrates a part of a stack 10 of sheets 11 to be counted bymeans of a counting rotor 12 of a known construction, which rotor formsno part of the present invention and will therefore not be described infurther detail here. The rotor may take the form of that counting rotordescribed in our co-pending International Patent Application filed inour name contemporaneously herewith, and claiming priority from93GB-12614.2. The rotor 12 is mounted on a shaft 13 which is supportedon a vertically-movable carriage (not shown) so that the rotor may beadvanced in the direction of arrow A, along the height of the stack ascounting progresses.

The sheets 11 in the stack 10 are clamped to a table 14 by means of aclamping pad 15 arranged to bear down on the top sheet 16 of the stack10. Any suitable means for urging the pad 15 into engagement with thestack so as to exert a required pre-determined force on the stack may beemployed. For example, the pad 15 may be mounted on and driven by apneumatic ram, or on a lead screw driven by a motor, or by spring means.

In use, both the rotor 12 and the clamping pad 15 are lifted clear ofthe support table 14 so that a stack 10 of sheets may be assembledthereon. Both the rotor 12 and clamping pad 15 are then advanced toengage the top sheet of the stack, the pad being urged to engage the topsheet with a pre-determined clamping force. Rotation of the rotor 12 maythen commence, to transfer sheets to the other side of the rotor, therotor being advanced in the direction of arrow A, as countingprogresses.

Control of vertical movement of the rotor is effected by the controlarrangement illustrated in FIGS. 2 and 3. The rotor 12 is mounted bymeans of a non-rotatable linear bearing (not shown) on shaft 13 which isdriven by a motor 35 mounted on a vertically-slidable carriage 36. Arelatively light spring 37 acts between the rotor 12 and a flange 38 atthe free end of the shaft 13, to urge the rotor 12 upwardly. A secondspring (not shown) may be disposed above the rotor 12, so that the rotoris balanced therebetween. A linear potentiometer 39, having a plunger40, is mounted on the carriage 36 so that the plunger bears on andsenses the position of the rotor 12, with respect to the carriage 36.

The carriage 36 is mounted on a pair of parallel guides 41 (only one ofwhich is visible in FIG. 2) for vertical sliding movement. The carriageincludes a nut 42 threaded on a lead screw 43 driven by a motor 44,whereby the vertical position of the carriage 36 may be adjusted asrequired, by driving the motor 44. Alternatively a motor andtoothed-belt or other non-slip drive arrangement could be employed toeffect movement of the carriage. Limit switches 45 and 46 for thecarriage are provided at each end of the guides 41.

FIG. 3 is a block diagram of the control circuit for the arrangementillustrated in FIG. 2. A power supply 50 is arranged to drive motor 44at a speed dependent upon input 51 to that power supply. The sensor 39provides feedback to the input 51 of the power supply, whereby the speedat which the motor 44 is driven depends upon the sensed position of therotor 12. The input 51 also is controlled by an external signal 52, forexample derived from a key pad and converted to an analogue signal byD/A 53, for example to control the maximum and minimum speeds ofoperation of the motor 44. Limit switches 45 and 46 are arranged toinhibit motor operation in the same sense as triggered the respectivelimit switch, so that once triggered, the motor may be operated only inthe reverse sense. A further control input 54 is provided to start andstop a counting operation.

Instead of the provision of a second spring, the rotor may be balancedbetween spring 37 and a spring force exerted by a sliding foot engagedwith the upper side of the rotor, to permit the connection of alow-pressure source to passages in the rotor, to assist with thetransfer of sheets from one side of the rotor to the other, during acounting operation. Such an arrangement is shown in FIG. 4.

A foot 60 is urged by a plunger 61 downwardly into engagement with theupper surface 62 of the rotor 12, by means of a spring 63 acting betweena shoulder on the plunger 61 and a housing 64 mounted on the carriage36. The plunger has a rounded lower end which is received in a conicalrecess in the foot 60, so that the foot may make good contact with theupper surface of the rotor and yet is accurately located by the plunger.A vacuum pipe 65 is connected to a low-pressure source and leads intopassageways (not shown) in the foot, to communicate with furtherpassageways in the rotor 12, as the rotor rotates.

At the upper end of the housing 64, there is a position detector 66 forthe upper end of the plunger 61. This position detector provides anelectrical output dependent upon the vertical position of the plunger,which output effectively comprises the signal of block 39 of the controlcircuit.

The control arrangement of FIGS. 2 and 3, and of FIGS. 3 and 4, ensuresthat the carriage 36 is advanced more or less continuously and smoothlyas a counting operation proceeds. By providing sufficient gain in thecontrol circuit, the carriage movement may accurately track theadvancement of the rotor through the stack, so that a near-constantforce is exerted between the rotor and the sheets of the stack.

I claim:
 1. Control means for a linearly-movable carriage supporting acounting head arranged to count each sheet in a stack of sheets, whichcounting head engages an edge region of the stack at one end thereof andthen is advanced through the stack to transfer sheets, one at a time, tothe other side of the head and generating a count on each said transfer,the counting head being movable with respect to the carriage generallyin the direction of movement of the carriage, which control meanscomprises a motor to effect carriage movement, a linear sensor forsensing the relative position of the counting head with respect to thecarriage, and a control circuit for the motor and arranged to cause themotor to run at an appropriate speed in response to an output of thesensor, whereby the carriage is advanced substantially constantly and atsubstantially the same rate as the counting head advances along thestack.
 2. Control means as claimed in claim 1, wherein the sensor isselected from the group consisting of a linear potentiometer and a LVDT.3. Control means as claimed in claim 1, wherein the control meansincludes limit switches for carriage movement, to inhibit motoroperation both when the carriage has been fully lifted away from a stackand when a counting operation has been completed.
 4. Control means asclaimed in claim 1, wherein the control circuit further includes acontrol permitting selection of an appropriate advance rate for thecounting head.
 5. Control means as claimed in claim 1, wherein thecarriage is slidably mounted on at least one guide therefor, the guideextending substantially parallel to the edge of a stack of sheets to becounted.
 6. Control means as claimed in claim 1, wherein the countinghead includes a rotor arranged to engage in the edge region of the stackof sheets, and to transfer the sheets one at a time from one side of therotor to the other side thereof upon rotation of the rotor.
 7. Controlmeans as claimed in claim 6, wherein the rotor is mounted on a shaftsupported by the carriage, the shaft being drivingly connected to therotor but the rotor being movable axially with respect to the shaft. 8.Control means as claimed in claim 7, wherein the rotor is mounted on theshaft by a non-rotatable linear bearing.
 9. Control means as claimed inclaim 7, wherein the rotor shaft extends substantially vertically andthe rotor is supported on that shaft by a spring.
 10. Control means asclaimed in claim 9, wherein means are provided to provide a downwardbias to the rotor.
 11. Control means as claimed in claim 10, wherein thedownward bias is provided by a foot assembly bearing on the rotor andarranged to couple a low-pressure source to the rotor.
 12. Control meansfor a sheet counter comprisinga carriage; at least one linear guide onwhich the carriage is mounted for linear sliding movement; a countingrotor mounted on the carriage for movement with respect theretogenerally in the direction of sliding movement of the carriage, therotor having first and second sides and arranged to engage an edgeregion of a stack of sheets to be counted, the rotor being configured totransfer sheets one at a time from the first side of the rotor to thesecond side thereof upon rotation of the rotor and a count signal beinggenerated on each such transfer; a motor to effect linear slidingmovement of the carriage; a linear sensor to sense the position of therotor relative to the carriage; and a control circuit for the motor andarranged to cause the motor to run at an appropriate speed in responseto an output of the sensor, whereby the carriage is advancedsubstantially constantly and at substantially the same rate as the rotoradvances along the stack during the rotation of the rotor.